Taste controls an animals food intake. For the past two decades, our focus has been the isolation and characterization of genes encoding taste receptors and using these to mark the cells, define the corresponding signaling pathways, dissect receptor specificity, generate topographic maps, and trace the respective neuronal connectivity circuits. This research continues to involve a long standing and wide ranging collaboration with Charles Zuker and his groups at Columbia University. Together, we have now established that at the periphery there are 5 distinct classes of taste receptor cells that are selectively tuned to respond to sweet, bitter, sour, sodium salt and savory (umami) tastants and have demonstrated that activation of these cells elicit either appetitive or aversive responses accordingly. Taste information is transmitted to the nucleus of the solitary tract (NST) in the hind-brain through sensory neurons with cell bodies in the geniculate and petrosal ganglia. Projections from the NST diverge: conscious perception of taste quality is thought to involve a pathway that innervates the primary gustatory cortex in the insula; in addition, less well characterized circuits are believed to mediate immediate responses to tastants. Our current work focuses on understanding how taste information is transmitted to the brain and represented there to generate defined percepts and to guide behavior. We are using a battery of modern molecular genetic approaches to define and trace circuits involved and ultimately to relate these circuits to taste perception. These include: Ca-imaging techniques to assess the activity of neural ensembles; screening and sequencing approaches to identify markers for select subsets of taste responsive neuron; and optogenetic, pharmacogenetic, activation and silencing as well as other silencing and ablation approaches to modulate activity of specific parts of the taste circuitry. In this reporting period we have used functional imaging to demonstrate the tuning specificity of taste primary afferents. In effect, these neurons faithfully transmit the signal encoded at the level of the tongue and closely match the tuning of the taste receptor cells. We have also been studying how taste-representation in the brain encodes quality and valance. In mice, the odorant receptors are encoded by a family of more than 1000 genes. A fundamental feature of the mammalian olfactory system is that each olfactory sensory neuron expresses just a single member of this vast family of genes. However, the details of the control of odorant receptor gene expression remain unexplained. In a collaborative project with Leonardo Belluscio, we have demonstrated new aspects of regulation that contribute to the control of odorant gene expression and have devised a system that can reliably generate mice expressing a single odorant receptor in the vast majority of olfactory sensory neurons. Over the past year we have continued to characterize a transgenic mouse that expresses an octanal receptor in almost all olfactory sensory neurons. Although this transgenic mouse line has the potential to express a second olfactory receptor from the same synthetic promoter as the octanal receptor, surprisingly it rarely does. Indeed, whereas the octanal receptor is found in 90% of all olfactory receptor neurons, the other receptor (that responds to acetophenone) is present in just 5% of cells and these do not overlap with the cells expressing the octanal receptor. We are using deep sequencing strategies in the hope of uncovering the mechanisms that account for this completely unexpected gene expression pattern and believe that they will provide insight into the unusual expression pattern of this remarkable gene family of sensory receptors.